The present invention concerns video display devices and in particular an active matrix organic light-emitting diode display which can operate either by clearing the pixels of the display device one row at a time or by clearing all of the pixels in the pixel array in a single operation.
An active matrix display device is one in which image data is stored in each picture element (pixel) of the display and the image is illuminated for a substantial part of the frame interval. There are two basic active-matrix display architectures. The first is a xe2x80x9crow at a timexe2x80x9d architecture where the image is updated one line at a time, as it is being displayed. In this architecture, a single row of the pixels is cleared and set-up to receive new data values and then a new line of data is written into the cleared pixels. The process repeats continually with each line of the image being updated at least once in a frame interval.
The second type of display architecture clears and sets-up the entire image in a single operation and then quickly writes new image data into all of the pixels one line at a time. This type of display operates in four distinct intervals: clear, set-up, write and illuminate. A display architecture of this type is particularly appropriate for use with a color shutter or other device where the entire pixel array is turned off for some fraction of the frame time.
Organic light emitting diode (OLED) displays are formed from a matrix of OLED devices. These devices emit light in response to an electric current. The intensity of the light is a function of the amplitude of the current. U.S. patent application Ser. No. 09/064,696 entitled ACTIVE MATRIX ORGANIC LIGHT EMITTING DIODE PIXEL STRUCTURES describes an exemplary OLED color matrix display device which controls the current through each OLED pixel by storing a voltage on a capacitor in the pixel cell. As described in this patent, each OLED device is discharged, autozeroed (i.e. set-up to receive new data) and then loaded with the new data.
As the number of pixels in a display increases, both the horizontal and vertical scan rates also increase so that the sequence of images can be displayed at a constant frame rate. As the horizontal scan rate increases, less time is available to update each row of pixels in the display. Existing row-at-a-time architectures are not well suited for high resolution OLED displays because it is difficult to discharge, autozero and load a row of pixel data in one line time at the scan rate of, for example, a high-definition television receiver.
The present invention is embodied in a row select circuit for an organic light emitting diode display. The row select circuit propagates a gating pulse through the shift register. This gating pulse is synchronized with a system clock signal and is used to apply a plurality of broadcast control signals, to sequentially selected rows of pixels on the display.
According to one aspect of the invention, the line scanning circuitry is controlled to clear and autozero the pixels in the display either one line at a time or the entire image array may be autozeroed concurrently.
According to another aspect of the invention, the clearing and autozeroing of a row of pixels in the display may be performed over several line intervals before the row is loaded with new values. This overcomes the problem of reduced scan time available in high resolution displays.
According to yet another aspect of the invention, the broadcast control signals may be adapted to achieve the best performance for each display device.